Pilot study work was completed, and nationwide enrollment began in October 2004. A total of 50,000 sisters of women who had breast cancer will be enrolled. At enrollment, the participants answer questions about life history, health, jobs and environment;and give samples of blood, urine, toenails, and housedust. The participants will be followed for at least 10 years. Data and samples from women who develop breast cancer will be compared to those for the majority who won't. Analyses will look for environmental associations with risk. Contract is on budget, and contractor is performing satisfactorily. See Annual Report for Dale Sandler for full progress report. Keywords breast cancer;sister;prospective epidemiologic study;environment;genes;exposures;blood;toenails;occupation;dust;urine;questionnaires